Technology for manipulating digital video has progressed to the point where it can be readily processed and handled on computers. For example, the Avid/1 Media Composer, available from Avid Technology, Inc. of Tewksbury, Mass., is a system wherein digital video can be readily captured, edited, and displayed for various purposes, such as broadcast television and film and video program post-production.
The Avid/1 Media Composer uses a media pipeline to provide real-time digital video output on a computer display. This media pipeline 30 is shown in FIG. 1 in is described in more detail in U.S. Pat. No. 5,045,940, issued Sep. 3, 1991. In this media pipeline 30, a permanent storage 40 stores sequences of digital still images which represent digital video and are played back at a rate which provides the appearance of video. The sequences of digital still images do not include any frame synchronization or other type of timing information which are typically found in television signals. The still images also typically are stored in compressed form. The stored sequences are accessed and placed in a data buffer 42 from where they are provided to a compression/decompression system 44. The output of the compression/decompression system 44 is applied to a frame buffer 46 which converts the still image to a typical video signal which is then applied to an input/output unit 48. Each of the systems 40, 42, 44, 46, and 48 in this media pipeline 30 operate bi-directionally. That is, the output process discussed above can be reversed and video signals can be input via input/output unit 48 to the frame buffer 46 where they are converted to a sequence of digital still images. The images in the sequence are compressed by compression/decompression system 44, stored in data buffer 42 and then transferred to the permanent storage 40.
In such a system, only simple effects such as cuts and fades, involving only one stream of video information, can be made. More complex, arbitrary digital video effects, however, especially three-dimensional effects, are typically provided by creating the effects using another system (described below with FIG. 2), and then storing the created effect in the permanent storage 40. A variety of systems are available for performing such three-dimensional digital video effects. Such a system is commonly called an on-line controller (OLC). An example of an OLC is found in U.S. Pat. No. 5,119,432, issued Jun. 2, 1992.
A block diagram of a typical OLC 55 is shown in FIG. 2. An OLC 55 typically uses digital video signals, which include frame synchronization and other timing information. Therefore, they typically require frame buffers such as shown at 50,54 and 56 to store the video signals being processed. The OLC 55 also includes a digital video effects DVE unit 52 which performs the desired effects. The DVE unit 52 has first and second inputs 51 and 53 which are connected respectively to outputs 57 and 59 of frame buffers 56 and 50. The DVE unit 52 has an output 61 which is connected to an input 63 of frame buffer 54. Input video sources 65 and 67, such as video tape decks, respectively provide video signal outputs 69 and 71 which are applied to inputs 73 and 75 respectively of frame buffers 56 and 50. The output 77 of the frame buffer 54 is applied to an output video storage 79, such as a video tape deck. One problem with such a typical OLC 55 is that it is not capable of being stopped during the process of creating the effect, because it operates using full-rate video signals.
Because of the complex hardware required to deal with video signals, in particular the frame buffers 50, 56 and 54, an OLC 55 is also typically expensive. Thus, producing complicated arbitrary three-dimensional video effects has not been possible in common consumer-oriented multi-media editing products.
Also, the process of preparing and editing such effects is time-consuming and, therefore, expensive. With standard OLCs, an effect is created by preparing two video tapes as input video sources 65 and 67 to provide the input video signals. These tapes must be synchronized together. Then, an output tape is prepared as the output video storage 79 to receive the output effect. The effect is then created using the DVE unit 52 by playing the input video tapes through the DVE unit 52 and recording the result on the output tape. In order for the editor to see the resulting effect, the output tape must be played back. If the result is not what is desired, the process must be repeated after appropriate adjustments are made. The repetitive recording/playing/adjusting cycle is costly.